Particulate CEMs for Wet and Dry FGD applications

Introduction
This paper overviews the challenges of monitoring particulate in wet and dry stack conditions found after wet and dry FGD arrestment plant fitted to coal fired power plant. It describes the techniques used for monitoring particulate in these applications and provides results and incites from the operation and calibration of PCME’s wet stack PMCEM in a wet FGD installation. 

The uptake of wet Flue Gas Desupherisation (FGD) technology in the power industry has created a new demand to continuously monitor particulate emissions due to the challenge of low dust concentration measurement and, in applications without reheat, the need for operation in ‘wet stack’ conditions. Wet conditions are more challenging to continuously monitor than ‘dry or non condensing’ stack conditions due to problems of overcoming interference from water droplets. Traditional particle measurements cannot be used in these applications due to interference from condensed Water vapour. There are essentially two core techniques for monitoring particulate emission concentration with high accuracy in wet stacks and both are extractive in nature (ie a sample is drawn continuously from the stack in a representative fashion) and passed through the analyser before return to the stack.

1) Beta Attenuation
2) Extractive light scatter

In the second type, the extracted stack sample is heated to evaporate any residual water droplets. Thus the sample becomes effectively dry so that it may be analysed by a standard dry measurement technique.